Protection of feeders of electrical distribution systems.



P. V. HUNTER. PROTECTION OE FEBDERS OF ELECTRICAL DISTRIBUTION SYSTEMSAFPLIGATION FILED 0017,1912

1,09 1,225. Patented M51124, 1914.

WWNBSSES= PHILIP VASSAR HUNTER, OF HEATON, ENGLAND.

PROTECTION OF FEEDERS OF ELECTRICAL DISTRIBUTION SYSTEMS.

Specification of Letters Patent.

Patented Mar. 24, 1914.

Application filed Gctober 7, 1912. Serial No 724,343.

that the said switches shall ren'iain inoperm tive whatever may he thecurrent passing through the feeder under normal conditions.

In a preferred form of my invention I make the core of the feeder anumber of strands and lightly insulate two of these strands from oneanother and from the main part of the core of the cable. Such main partI shall hereinafter refer to the main core. The insulation between thetwo strands, hereinafter referred to the balancing stran need not bemore than merely sutlicient to Withstand the XIIOIUOIL tary voltagewhich may occur between the strands and between them and the main coreduring the time that the switches take to operate on the occurrence ofleakage. The said balancing strands are designed to convey a smallportion of the feeding cur rent such small portion being equal in eachbalancing strand. One of the said balancing strands is electricallyconnected to the main core at one point in itsilengi'h If equalsensibility of the automatic gear is required at both ends of the feedcrthe point of connection should be midway between the ends.

in order that my invention may be more readily grasped i. shall proceedto describe it, with reference to the acccunpanying uia grams whichillustrate the main principle of no invention and how it may he carriedinto effect.

in the drawings Figure 1 represents one form of my intention and Fig. 2,another form;

In Fig. 1 of the said diagrams, 1 is the main core and 2, 2 switchesorcircuit breakers, placed one at each end of the feeder, which aredesigned to he ripped or opened on leakage, in the feeder taking place.

3, 4 are the balancing strands one of which, 3, is electricallyconnected (as diagran'imatically shown by the conductor with the maincore 1. l

6, 6 are ditfe'cntial electromagnetic devices which in the case ofalternating currcnt systems are preferably balancing transformers of akind described in the specification accompanying my application forLetters Patent of the United States, filed 31st July 1911, under. serialNo. (341,511.

7, T are solenoids connected with the balancing transformers asshown and8, S are the solenoid cores or extensions thereof serving to open ortrip the switches 2, 2.

The action is as follows: Let us assume current is flowing from thepoint 2 along the feeder 1 to the point. 2. There is a gradual anduniform drop of potential along the main core between 2 and 2. Whatismore there is a similar gradual and u'niforn'i drop of potential from2 to 2 along the strand and from 2 to 2 along the strand 4. There beingno difference of potential, then, between corresponding or contiguouspoints of the wires, 1, 3 and 4, there is, under normal conditions, nocurrent in the connecting conductor 5 and, the resistances of the wires3 and 4 being the. same, there is as much currentin 3 as in 4. Thismeans the transformers G and 6' are balanced and that no current isinduced in the coils 7 and 7. The switches 2 and 2 thus remain closed.Assume now that there is a leak or ground between the point 2' and theconductor 5) on the main feeder 1. Clearly there is an additional pathestablished for current through the wire 3: not only'the original pathfrom 2 through both transformer coils to 2' but also a new path from 2through thc conducter to' arth. There is, however, no new pathestablished for the current through the wire 4. Hence the sann amount ofcurrent will no longer flow in the strands 3 and 4; the transformers .land 6 will become unbalanced, current will be induced in the coils 7 and7. the cores 8 and 8' Will he magnetized and the switches 2 and 2 willbe opened to cut the grounded feeder out of the distribution system,

Fig, 2 of the accompanying diagrams illustrates a modification in whichresistances are used if the system be of the more usual direct currentvariety and impedances 9, 9 are used it an alternating current system beemployed. In either case, I call tl'iese parts current obstruct-ore andthey are inserted between the ends of the main core of the feeder 1, andthe switches 22, 2. I have found thatby this means I increase thesensitiveness to faults near the end of the feeder. Without theseresistances or impedances the sensitiveness in the case of a fault isgreater (in the case shown in Fig. 4) at the middle or the point ofconnection of the conductor 5 and decreases toward the' switches :2, 2'.When however the resistances or impedances are in circuit as shown thesensitiveness does not fall below a given value at any point of thefeeder.

It will be seen that when there is no leakage from the main core theswitches will not be operated as the currents in the two balancingstrands will be equal.

To prevent any inequality of current in the two balancing strands due toinduction I prefer to twist them relatively to the main core of thefeeder cable in a well known manner.

It is not necessary but as hereinbcfore stated it is desirable} that thebalancing strands should be in fact strands forming part'of the samecable core with the main core of the feeder cable. They might instead beseparate parallel insulated conductors taking their desired proportionsof the total feeding current. I howeverprefer to strand and twist theconductors as hereinbefore mentioned. Nor is it necessary that theelectrical connection between one of the balancing strands and the maincore should be by a distinct conduct-or as In practice such connectioncould be made by more absence of insulation at a point of contact. Thusat the point of connection the insulation might be cut away for a smalldistance and the bare cornluctors brought together and maintained inContact by a clip or ligature or the like, a suitable insusting coveringbeing then put over the joint for protection. I may also make up anumber of cores with balancing strands into a feeder cable.

1 use the term dilierential electromagnetic device to cover allelectromagnetic devices controlled by two currents which becomeeffective when the normal flow of the two currents is sutlicientlychanged. The term bal ancing transformer indicates a type ofdifferential electromagnetic deuce especially usable for alternati..gcurrents in which two primary coils, wound on the same transfl ner core,normally counteract each other, but cease to do so when the normal flowof the currents in these'primary cells is sufficiently changed, in whichcase the secondary coil becomes active.

1 have clearly defined the meaning of the terms ditlerentialelectromagnetic device and balancing transformer, although I submit thatthese are terms well understood in the art. So, too,-I am aware thatthere exist many kinds of differential electromag netic devices, in arclamps, in telephone receivers, in railroad signal systems, in callsystems and so on. My claims do not rely upon the specific constructionof the dillerential device but cover broadly the use of any such devicein connection with the balancing strands, the main core and the'circuitbreaker.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is 1. In an electrical distribution system, amain core, a circuit breaker therein, two balancing strands connected tothe core at their ends and one of which is electrically connected withthe main core at an interme diate point, and a differentialelectromagnetic device for actuating the circuit breaker controlled bythe balancing strands, substantially as described.

2. In an electrical distribution system, a main core, a circuit breakertherein, two balancing strands connected to the core at their ends andone of which is electrically connected with the main core at anintermediate point, a current obstructor near the end of the main core,and a differential electromagnetic device for actuating the circuitbreaker controlled by the balancing strands substantially as described.

In an alternating current distribution system, a main core, a circuitbreaker therein, two balancing strands connected to the core at theirends and one of which is electrically connected with the main core at anintermediate point, and a balancing transformer for actuating thecircuit breaker controlled by the balancing strands substantially asdescribed.

4. In an alternating current distribution system, a main core, twocircuit breakers near its ends, two' balancing strands connected to thecore at their ends and one of which is electrically connected with themain core between its ends, and two balancing transfrn'mers foractuating the circuit breakers controlled by the balancing strands,substantially as described.

In witness whereof I have signed my name to this specification in thepresence of two subscribing witnesses.

PHILIP VASSAR HUNTER.

Vii tncsscs H. Nixon. Fnan ll. Dunn.

